1. Field of the Invention
The present invention relates to a multiple-ring communication system which includes a plurality of nodes intercoupled in at least two rings and operating on an equal basis without central control, each node including a plurality of message receiver/transmitter equipments associated to distinct ones of said rings respectively and able to receive messages on said rings and transmit messages thereon in opposite directions, and processing means for checking the receipt or absence of receipt of signals on the receiver ring portions connecting the receivers of said node to transmitters of its neighbouring nodes and for performing reconfiguration operations in response to the result provided by said checking operation.
2. Description of Related Art
Such a system is already known from the article "A distributed double-loop computer network (DDLCN)" by J. J. Wolf and M. T. Liu, published on pages 6-19 to 6-34 of the Proceedings of the Seventh Texas Conference on Computing Systems, held in Houston, Oct. 30-Nov. 1, 1978.
In order to have a maximum number of nodes always able to communicate with each other, even when there is some fault in the system, it is necessary to test the condition of the system almost continuously and in case an error is detected to take immediately the necessary reconfiguration measures to restore the faulty system back to an operative status. Such a reconfiguration measure consists for instance in case of an interruption for both rings, in transforming the double ring system into a single ring system by establishing two interconnections between these rings.
In the above mentioned known system each node transmits to its neighbouring nodes timing signals as long as it is not transmitting messages, so that each node receives such timing signals substantially in a continuous way on the receiver ring portions by means of which its receivers are coupled to the transmitters of the neighbouring nodes. Each node tests the condition of its neighbouring nodes by checking the receipt or absence of receipt of these timing signals. In this way very limited information is obtained at the testing node on the overall status of the system since this information only concerns the condition of the receiver ring portions, of the transmitters of the neighbouring nodes and of the own receivers. No information at all is obtained at this node on the condition, for instance of its own transmitters, of the receivers at the neighbouring nodes and of the transmission ring portions by means of which its transmitters are coupled to receivers at the neighbouring nodes. As a consequence, reconfiguration measures have to be taken by the processing means on the basis of very limited information on the system status and these measures can therefore be erroneous. For instance, it might be decided to establish two loops between the rings to form a single ring system although one of the rings is still fully operational.
An object of the present invention is to provide a multiple-ring communication system of the above type, but each node of which is adapted to collect more information on the status of the system.